isl_map_intersect: fix error handling
isl_map_intersect: fix error handling

The original code would simply drop basic sets that resulted in errors
instead of propagating the error to the caller.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

KangDroidSMProject/ISL,inducer/isl-mirror,pierrotdelalune/isl,tobig/isl,UBERTC/isl,serge-sans-paille/isl,SaberMod/isl-current,BenzoSM/isl,Distrotech/isl,Meinersbur/isl,VanirLLVM/toolchain_isl,Distrotech/isl,inducer/isl-mirror,BenzoSM/isl,epowers/isl,inducer/isl-mirror,Meinersbur/isl,cfx-next/toolchain_isl-upstream,epowers/isl,serge-sans-paille/isl,abduld/isl,jleben/isl,nicolasvasilache/isl,BenzoSM/isl,tobig/isl,serge-sans-paille/isl,BobSaget-Mod/libisl,abduld/isl,BobSaget-Mod/libisl,PollyLabs/isl,pierrotdelalune/isl,KangDroidSMProject/ISL,crossbuild/isl,abduld/isl,nicolasvasilache/isl,VanirLLVM/toolchain_isl,serge-sans-paille/isl,SaberMod/isl-current,inducer/isl-mirror,nicolasvasilache/isl,cfx-next/toolchain_isl-upstream,serge-sans-paille/isl,VanirLLVM/toolchain_isl,jleben/isl,VanirLLVM/toolchain_isl,jleben/isl,crossbuild/isl,crossbuild/isl,Distrotech/isl,KangDroidSMProject/ISL,jleben/isl,Distrotech/isl,UBERTC/isl,BenzoSM/isl,PollyLabs/isl,UBERTC/isl,simbuerg/isl,cfx-next/toolchain_isl-upstream,nicolasvasilache/isl,nicolasvasilache/isl,SaberMod/isl-current,SaberMod/isl-current,inducer/isl-mirror,Meinersbur/isl,BobSaget-Mod/libisl,cfx-next/toolchain_isl-upstream,epowers/isl,simbuerg/isl,PollyLabs/isl,pierrotdelalune/isl,BenzoSM/isl,VanirLLVM/toolchain_isl,tobig/isl,pierrotdelalune/isl,PollyLabs/isl,pierrotdelalune/isl,crossbuild/isl,epowers/isl,BobSaget-Mod/libisl,jleben/isl,abduld/isl,BobSaget-Mod/libisl,evaautomation/isl,Distrotech/isl,evaautomation/isl,Meinersbur/isl,PollyLabs/isl,simbuerg/isl,simbuerg/isl,evaautomation/isl,epowers/isl,KangDroidSMProject/ISL,cfx-next/toolchain_isl-upstream,simbuerg/isl,KangDroidSMProject/ISL,tobig/isl,evaautomation/isl,UBERTC/isl